Tunnel magnetoresistance (TMR) effect was discovered in 1975. This effect was observed in a magnetic tunnel junction consisting of two ferromagnets and a tunnel barrier sandwiched between the two ferromagnets. Since then, magnetic tunnel junctions have been studied and developed for different electronic applications. Two important applications based on magnetic tunnel junctions among others are the read-heads of hard disk drives and a new type of non-volatile memory MRAM (magnetic random access memory). In order to satisfy exponentially increased demand of high storage capacity and low cost, industry usually tends to shrink the line width, pitch and film thickness (technology node in general) within electronic devices, thereby increasing device density in a single chip and reducing the cost per chip. However, when the shrinkage is approaching physical limits, the industry faces a dilemma. What's needed is a new design that can increase device density while keeping the chip size and technology node.